This invention relates to a method for preparing a multilayered belt, more particularly, to a method of preparing a photoreceptor belt using a rotatable mandrel.
Generally, photoreceptor belt fabrication systems require considerable space for equipment and processing. For coated belts, elaborate handling procedures and machinery are needed to manipulate the belts between stations where successive coatings are applied to the substrate belt. Such handling between coatings increases the likelihood of damage due to scratches, creases, folds, fingerprints, dust contamination and the like which reduce overall yield and increase cost.
Photoreceptor belts typically have thicknesses greater than about 10 mils and are usually formed by molding or lamination. Molding is carried out in molds, which often results in flashings which must be removed to achieve smooth outer surfaces. Lamination may alternatively be employed to form photoreceptor belts. Lamination may be accomplished by applying alternate layers of thermoplastic sheets and reinforcing fabrics. Other types of belts have been prepared by welding opposite ends of sheets together to form belts having seams.
In the past, photoreceptors for electrophotographic imaging systems have employed selenium alloys vacuum deposited on rigid aluminum substrates. These photoreceptors require elaborate, highly sophisticated, and expensive equipment for fabrication. Photoreceptors have also been prepared by coating rigid substrates with photoconductive particles dispersed in organic film-forming binders. Coating of rigid drum substrates has been effected by various techniques such as spraying, dip coating, vacuum evaporation, and the like. Rigid drum photoreceptors limit apparatus design flexibility and flash exposure and are expensive.
Flexible organic photoreceptors in the form of belts have recently become commonplace. Flexible photoreceptors have been manufactured by coating a web and thereafter shearing the web into segments which are formed into belts by welding opposite ends of the sheared web. The resulting welded seam on the photoreceptor disrupts the continuity of the outer surface of the photoreceptor and must be indexed so that it does not print out during an imaging cycle. Efficient stream feeding of paper and throughput are adversely affected in such systems because of the necessity to detect a seam within the length of each sheet of paper. The mechanical and optical devices required for indexing add to the complexity and the cost of copiers and printers, and reduce the flexibility of design. Welded belts are also less desirable for electrophotographic imaging systems because the seam forms a weak point in the belt and tends to collect toner debris during cleaning, particularly with wiper blade cleaning devices.
U.S. Pat. No. 4,747,992 (incorporated herein by reference) is directed to a process for fabricating a seamless belt in which a substrate layer is formed on a mandrel by coating a polymeric film-forming material, which is then solidified. Additional layers may be applied to the substrate to provide layers needed for photoreceptors.
Important considerations in manufacturing photoreceptors by applying layers onto a substrate on a mandrel include providing precise dimensions, particularly the interior circumference of the substrate, ensuring that the substrate is tightly held on the mandrel while applying the layers ease of removal of the multilayered product from the mandrel and commercial production considerations, such as simplification of the process and increased speed of production.
In the method according to U.S. Pat. No. 4,747,992, after solidifying the polymeric coating on the mandrel, both the solid coating and the mandrel are heated to a temperature at least above the apparent glass transition temperature (T.sub.g) to expand the coating and the mandrel while maintaining contact between the coating and the mandrel. The solid coating is then cooled to below the apparent T.sub.g, after which the mandrel is cooled, such that the mandrel contracts at a greater rate than the polymeric coating, until separation occurs between the mandrel and the coating. The coating is then removed from the mandrel.